PRACTICAL PAPERS — VEGETABLE MATTER , ETC . 361 
nature’s primeval laboratories, where matter is prepared for subse¬ 
quent use. Here the material of the two kingdoms is the same, 
and exists only under physical and chemical laws. The object of 
this department is, first, to work up this mass of elementary mate¬ 
rial into forms of matter we call minerals, preparatory to being 
worked up into forms we call vegetables and animals. In fact, the 
great work of the mineral kingdom is, to take this raw material 
and work it up into forms and conditions adapted to the wants 
of the vegetable kingdom. 
If we pause a moment here, and look down into the furnace of 
this laboratory, where the heat is most intense, we shall find that, 
as the temperature is gradually lowered, the free elements of silica 
are uniting to form quartz. In the same igneous mass, we notice 
the elements of feldspar, mica and hornblende, arranging themselves 
also, under crystalline influence into distinct minerals, which at 
a subsequent stage of cooling are aggregated into a rocky mass, 
and laid aside as a portion of the crust of the earth. In this way, 
and by this process, the minerals of our plutonic rocks have been 
formed, and aggregated into masses of solid material, and spread 
out as unfinished forms of matter to be used again in a higher de¬ 
partment in nature’s factory, namely, the department of agriculture. 
It is very interesting to notice, that, in the great variety 
of minerals thus formed, and aggregated into rocky masses form¬ 
ing the crust of the earth, there are after all comparatively 
few elementary substances, and those such as are adapted to the 
wants of the vegetable kingdom. 
Among the elementary substances that enter to any great ex¬ 
tent into these plutonic or granitic rocks, are the following : Po¬ 
tassium, aluminium, sodium, calcium, magnesium, iron, manga¬ 
nese, silicon and oxygen. Other elementary substances may occa¬ 
sionally enter into their composition, but on a minor scale, and to 
a very limited extent. 
It is true, the varying' proportions in which these elementary 
substances enter into the composition of these minerals produce a 
variety in their forms, and we are in the habit of calling by dif¬ 
ferent names the rocks in which certain of these minerals prevail, 
or otherwise. But such is the family likeness, that we are safe in 
putting them into one class, and calling them granitic rocks. 
